Diverse forms of activity are potentially capable of improving mental health in a highly cost-effective fashion. Current treatments for mental illness are not universally beneficial and high-costs block their application to many people in need of help. In addition, well-being levels in the general population are not ideal with definite room for improvement. Hence, a highly cost-effective and robust strategy for both treating mental illness and advancing mental health in the general population is greatly needed. That strategy is activity! Physical, social, nature, cognitive, art/hobby, and music forms are applicable. Activity For Mental Health is the only book providing evidence and reasons for why these diverse types of activity both treat mental illness and advance mental health in the general population. Mental health providers, researchers, students, policy-makers, and consumers will benefit from the comprehensive review of studies and exploration for why each of these forms of activity, and activity in general, is so effective. Evidence levels are summarized revealing the current status of research efforts. The reasons accounting for the mental health benefits of activity are intriguing and ground the evidence in a scientific foundation.